Clearly it is A-Fib with a rapid ventricular response. From what I can see, the QRS interval is within normal limits, that and your axis is normal which rules out a left bundle branch block with aberant conduction. The best thing I can come up with based on what I can see is A-Fib with a rapid ventricular response and left ventricular hypertrophy. The hypertrophy would present with inverted ST segements, especially in AvL, V-5, V-6,, which your strip has. I don't see anything malignant here other than the rate.
